One of the most difficult problems in the treatment of cancer is acquired resistance to chemotherapy. Defects in DNA repair are likely to play a critical role in the sensitivity of cancer cells to chemotherapeutic drugs, many of which are DNA-damaging agents. Fanconi Anemia (FA) is a genetic disorder characterized by cancer susceptibility and cellular hypersensitivity to DNA crosslinking agents, such as cisplatin and melphalan. FA proteins and breast/ovarian cancer susceptibility gene products (BRCA1 and BRCA2) cooperate in a common DNA damage-activated signaling pathway (the FA-BRCA pathway), which controls DNA repair. We hypothesize that integrity of the FA-BRCA pathway is a critical determinant of resistance of tumor cells to chemotherapy with DNA crosslinking agents. The goals of our proposed research are 1) to elucidate the role of the FA-BRCA pathway in cisplatin sensitivity/resistance of cancer cells, 2) to determine if the sensitivity of tumor cells to DNA crosslinking agents can be increased by modulating the FA- BRCA pathway using small molecule inhibitors of the pathway, and 3) to further elucidate the mechanism of regulation of the FA-BRCA pathway. We plan to determine the role of one of the FA genes, BRCA2/FANCD1, in acquired resistance to cisplatin by analyzing BRCA2-deficient cancer cell lines and clinical samples of ovarian cancer. We also plan to identify small molecule inhibitors of the FA-BRCA pathway which sensitize tumor cells to DNA crosslinking agents. Several candidate chemicals including cyclin dependent kinase inhibitors and proteasome inhibitors have already emerged from our initial screens. We plan to test if these inhibitors sensitize cancer cells to cisplatin and ultimately to elucidate the mechanism of actions of these drugs. We also plan to elucidate involvement of cyclin-dependent kinases and the proteasome in the regulation of the FA-BRCA pathway using the inhibitors we identified. These studies will lead to discovery of potential drugs that can be used as chemo-sensitizers in the treatment of cancer, provide new insights about the signaling of the FA-BRCA pathway, and may eventually lead to establishment of a strategy to overcome chemo-resistance of cancer. Relevance: Our studies are intended to clarify why some cancers can be effectively treated with drugs that cause DNA damage and others become resistant. They should also lead to a discovery of ways to make cancer chemotherapy more effective.